Griffithsia complanata Huisman

Scientific Description

Habit and structure. Thallus erect, to 6 mm tall, attached by multicellular rhizoids arising from basal cells, complanate and dichotomously divided at every cell. Basal cell cylindrical, all others broader and elongate-cuneate. Apices straight or slightly curved and arching over the reproductive structures. Lower cells 300–360 µm diam. [L:B 2–2.5]; upper cells 250–300 µm diam. [L:B c. 2]; apical cells 100–150 µm diam. Trichoblasts rare, near apices, tri- to tetrachotomously branched, with elongate cells 5–8 µm diam. (including the wall).

Reproduction. Spermatangia formed in dense heads arising 2 or 3 on subapical cells, adjacent to a vegetative cell. Spermatangial heads involucrate (although the origin of the involucral cells could not be determined). Female fertile axes arising as half of a subdichotomy near apices, 3-celled; apical cell displacing slightly laterally; subapical cell bearing 2 periaxial cells, one of which acts as the supporting cell and bears one or two 4-celled carpogonial branches and a terminal sterile cell. Following presumed fertilisation the auxiliary cell arises distally from the supporting cell, and an involucre of 2-celled filaments develops from the hypogenous cell and surrounds the growing gonimoblast. Basal cell of involucral filaments inconspicuous, considerably smaller than the distal cell. Gonimolobes spherical, 3 or 4 arising from the auxiliary cell. Tetrasporangia not observed.

Distribution. Known only from Barrow Island, Western Australia.

[After J.M. Huisman in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 602–604 (2018)]